This chapter is for the Enterprise Bean provider; that is, the person in charge of developing the software components on the server side.
For container-managed transaction management, the transactional behavior of an Enterprise Bean is defined at configuration time and is part of the assembly-descriptor element of the standard deployment descriptor. It is possible to define a common behavior for all the methods of the bean, or to define the behavior at the method level. This is done by specifying a transactional attribute, which can be one of the following:
If the method is called within a transaction, this transaction is suspended during the time of the method execution.
If the method is called within a transaction, the method is executed in the scope of this transaction; otherwise, a new transaction is started for the execution of the method and committed before the method result is sent to the caller.
The method will always be executed within the scope of a new transaction. The new transaction is started for the execution of the method, and committed before the method result is sent to the caller. If the method is called within a transaction, this transaction is suspended before the new one is started and resumed when the new transaction has completed.
The method should always be called within the scope of a transaction, else the container will throw the TransactionRequired exception.
The method is invoked within the caller transaction scope; if the caller does not have an associated transaction, the method is invoked without a transaction scope.
The client is required to call the bean without any transaction context; if it is not the case, a java.rmi.RemoteException is thrown by the container.
This is illustrated in the following table:
| Transaction Attribute | Client transaction | Transaction associated with enterprise Bean's method |
|---|---|---|
| NotSupported | - T1 | - - |
| Required | - T1 | T2 T1 |
| RequiresNew | - T1 | T2 T2 |
| Mandatory | - T1 | error T1 |
| Supports | - T1 | - T1 |
| Never | - T1 | - error |
In the deployment descriptor, the specification of the transactional attributes appears in the assembly-descriptor as follows:
<assembly-descriptor>
<container-transaction>
<method>
<ejb-name>AccountImpl</ejb-name>
<method-name>*</method-name>
</method>
<trans-attribute>Supports</trans-attribute>
</container-transaction>
<container-transaction>
<method>
<ejb-name>AccountImpl</ejb-name>
<method-name>getBalance</method-name>
</method>
<trans-attribute>Required</trans-attribute>
</container-transaction>
<container-transaction>
<method>
<ejb-name>AccountImpl</ejb-name>
<method-name>setBalance</method-name>
</method>
<trans-attribute>Mandatory</trans-attribute>
</container-transaction>
</assembly-descriptor> |
In this example, for all methods of the AccountImpl bean which are not explicitly specified in a container-transaction element, the default transactional attribute is Supports (defined at the bean level), and the transactional attributes are Required and Mandatory (defined at the method-name level) for the methods getBalance and setBalance respectively.